disappearing chickens

So in the last 3 days 2 of our 4 month old chickens have vanished. We have had chickens in this coop for a year without any issues. I live in the Santa Ceuz mountains and am completely dumb founded and heartbroken. There are no feathers or evidence of something getting into the coop. What predators are really sneaky? Has anyone tried the motion activated predator deterrents? Or is there something we can spray to deter predators? Our coop is all wire, we will be covering the larger wire grate with a smaller grate to ensure nothing can stick its arm through or slither through. I am at a loss and any advise on protecing my flock will be greatly appreciated.